The present invention broadly relates to thread-guide rolls and, more specifically, pertains to a new and improved construction of a thread-guide roll for a thread supply device of a textile machine, especially for a thread brake device of an embroidering machine, in which the thread supply device comprises a freely rotatably mounted thread-guide roll couplingly engageable with a common brake or drive shaft and having a thread friction liner.
Generally speaking, the thread-guide roll of the present invention is for use with a thread supply device of a textile machine, especially for the thread braking device of an embroidering machine, wherein the thread supply device comprises a freely rotatable thread-guide roll for each thread to be braked or delivered, the thread-guide roll being operatively associatable with a common braking and driving shaft and having a thread friction liner.
For the generation of the necessary tension in threads or the like which are withdrawn from bobbins or packages by the processing or working tools of a textile machine, for instance by the operating or working needles of an embroidering machine, it is known to guide the threads each over a thread-guide roll and to centrally brake these rolls by a brake shaft common to all operating positions. This assures that the thread feed or supply to each processing position is the same independent of both the friction arising during processing and the tension of the thread between the brake shaft and the bobbin or package as well as other unequal or differing conditions for the individual operating positions. This, in turn, guarantees a product which is uniform over all processing or operating positions.
Switchable or engageable brake devices for this purpose are known in which, when engaging or disengaging individual operating positions, the associated processing tools are also simultaneously engaged with or disengaged from the brake shaft, for instance the rolls supplying threads to the individual needles in an embroidering machine. In such switchable or engageable brake devices known from the Swiss Pat. Nos. 515,372, 535,313 and 616,715, a lever carries a freely rotatable thread brake roll which can be coupled to or, for disengaging the operative connection, lifted away from the brake shaft by pivoting the lever by means of control devices which also engage or disengage the processing tools. In each operation or process cycle the corresponding processing tool draws the thread length necessary for the operation. At each such withdrawal of thread the entire system of brake shaft and thread brake roll is rotated to generate the required thread tension. In order that the tension to be generated not be altered by the thread slipping on its roll the latter is provided with a friction liner.
It has been found in practice that there is no known friction or brake liner which is suited to all thread qualities to be processed. Certain types of thread tend to slip on the usual brake liners, others show a marked tendency to climb up the side walls of the rotating roll, which not only detracts from their frictional contact with the brake liner of the roll but also in many cases finally leads to the thread falling out of the roll groove and to operational disturbances.